The invention relates chemical mechanical polishing of substrates, and more particularly to dispensing slurry onto a polishing pad and cleaning the polishing pad.
Chemical mechanical polishing (CMP) is a process by which a substrate surface is planarized to a uniform level. In a conventional CMP apparatus, substrate is mounted on a rotatable carrier head and pressed against a rotating polishing pad. An abrasive chemical solution (slurry) is applied onto the polishing pad to aid in the polishing of the substrate to achieve a desired surface finish. Over time, the polishing process glazes the polishing pad and creates irregularities in the polishing pad surface that can adversely affect the substrate surface finish. The polishing pad surface is typically "conditioned" by scouring the polishing pad surface with an abrasive device known as a conditioning disk to deglaze and roughen the polishing pad surface. Periodically conditioning the pad maintains the pad surface at a consistent state of roughness to achieve consistent polishing uniformity.
One problem encountered in CMP is the generation of contaminants on the polishing pad surface during the polishing and conditioning procedures. These contaminants have a material adverse affect on the polishing process. For example, contaminants include (but are not limited to) abraded polishing pad material, dried slurry particles, conditioning disk material and airborne contaminants. Adverse material effects include (but are not limited to) scratching of the substrate and embedding of the particles in the polishing pad or substrate. It would be advantageous if the polishing apparatus cleaned the polishing pad to provide a substantially contaminant-free polishing pad.
Another problem in CMP is that slurry is an expensive consumable. A CMP system may use more than two hundred milliliters of slurry per minute. In general, the substrate takes two to three minutes to polish. Thus, a CMP system can use up to a sixth of a gallon of slurry per substrate. The per substrate cost of CMP could be reduced considerably by reducing the amount of slurry used. In addition, where excessive slurry is applied, the substrate can hydroplane over the surface of the polishing pad, thereby reducing the polishing rate. It would be advantageous if the CMP apparatus that reduced slurry consumption in the polishing process.